1. Technical Field
The present invention relates to a technology of image processing which determines dot forming condition at the time of printing images constituted by plural pixels using dots of plural sizes.
2. Related Art
An ink jet printer is known as a printing device which forms dots on various types of printing medium such as paper, fabric, and film for printing images. The ink jet printer prints images on the printing medium by injecting ink in colors of cyan (C), magenta (M), yellow (Y), and black (K) to the printing medium and forming ink dots on the printing medium. There is such a type of ink jet printer which can form dots of plural sizes such as large dots (L dots), medium dots (M dots), and small dots (S dots).
At the time of printing images by using the ink jet printer, a process for determining dot forming condition for respective printing pixels is generally performed based on image data corresponding to images (referred to as half tone process) (for example, see JP-A-2007-118238). Determining the dot forming condition for the respective printing pixels corresponds to determining size and color of dots to be formed for the respective printing pixels (or whether dots are formed or not).
In the half tone process, limitation is set to the total ink amount per unit area of printing medium in some cases for preventing color blurring or for other reasons. In this case, there is a possibility that a mixture of dots of different sizes are formed for printing pixels constituting edge portions of characters and drawings in an image, or that no dot is formed for a part of the printing pixels, for example. As a result, the printing image quality deteriorates due to unstableness and lack of the edges.
These problems arise not only from image printing by using this type of ink jet printer but also from other devices when determining dot forming condition for respective printing pixels in case of image printing by using dots.